1. Field of the Invention
The present invention relates generally to mold-release agents for mold surfaces and, more particularly, to mold-release coating systems including wax-based barrier coats and release powders deposited on mold surfaces.
2. Description of Related Art
In the process of making molded polymeric foam parts, such as polyurethane foam parts, foam precursor material is first admitted into a mold and, subsequently, the foam precursor material is caused to foam and cure, taking on the shape of the mold's interior. It is commonplace to use a mold-release coating on the interior mold surfaces to facilitate removal of the cured foam part, especially in high-volume production applications.
Typically, the interior surfaces of the mold are coated with a wax mold-release agent before every molding operation. The wax mold-release agent allows complete and easy removal of the molded part. Generally, the wax mold-release agent is spray-applied onto the mold surface.
Current wax mold-release agents include solvent-based and water-based agents. Solvent-based wax mold release agents are applied to the interior surface of molds and allowed to dry. These agents are applied before every molding operation or frequently between molding operations. However, during the drying cycle, volatile organic compounds are emitted, requiring precautions to avoid human exposure.
Water-based wax mold-release agents result in substantially less emission of volatile organic compounds than do the solvent-based wax mold-release agents. Water-based wax mold-release agents are also applied before every molding operation or frequently between molding operations. Although they contain much less volatile organic compounds than solvent-based wax mold-release agents, water-based wax mold-release agents are not without problems.
One problem with water-based wax mold-release agents is that they still contain a small amount of volatile organic compounds that are emitted during the coating process. Secondly, water-based wax mold-release agents create a larger build-up on the mold surface causing undesirable changes in the mold's dimensions or contours. Thirdly, water-based wax mold-release agents are more expensive than solvent-based wax mold-release agents. Lastly, water-based wax mold-release agents require longer drying times than do solvent-based wax mold-release agents.
Furthermore, conventional solvent-based and water-based waxes, which typically contain only about 3–5 weight percent solids, require many applications to build up the wax coat to a suitable initial thickness.
Therefore, there exists a need for wax-based, mold-release coating systems that are inexpensive to manufacture, simple to use, and are environmentally-friendly.